Pae χψ binds to ssDNA. ( A ) Sedimentation coefficient of 35 μM poly(dT) in the presence of Pae χψ (diamonds), Pae χψ (Δ1-85) (squares) or Eco χψ (triangles) measured in low salt buffer at 20°C and 25000 rpm (λ = 280 nm). While the addition of Pae χψ increases the sedimentation coefficient of poly(dT) significantly, indicating the formation of a complex, Eco χψ shows only a slight effect. The binding of the truncated Pae χψ(Δ1-85) is severely reduced compared to wild-type, which shows that the N-terminus of Pae ψ is involved in ssDNA-binding. Lines are drawn just to guide the eye. ( B ) Binding isotherm for the Pae χψ/poly(dT) interaction, obtained by analysis of the c(s) distributions (see Methods section) of sedimentation velocity experiments at a (dT) concentration of 35 μM. The line represents a theoretical binding isotherm calculated for a simple interaction model of n molecules of χψ with one dT residue using the parameters: n = 0.12 and K = 5 × 105 M-1.